Both were hurt riding motocross, considered a vital but always risky element of training.
Gardner suffered a double leg fracture in an awkward landing from a jump in the week leading up to the Jerez race. He was riding at Montmelo outside Barcelona, close to his Sitges home.
Three days earlier Aegerter was enduro training when he fractured his pelvis, also requiring surgery.
Both will be out for an indeterminate time; with races coming at regular fortnightly intervals from now on.
Another Moto2 rider, Marcel Schrotter, was back on his bike, if painfully, after suffering ligament damage in a crash at the last round in Austin, Texas.
In MotoGP, Dani Pedrosa was closer to full recovery after his heroic ride in Texas with a freshly broken wrist; but rookie Hafizh Syahrin was battered and bruised after a high-speed cycle crash.
Motocross or other off-road training has claimed a number of high-profile victims at regular intervals. Rossi is one, spoiling one whole season after a shoulder injury back in 2010, and almost missing last year’s Italian GP after a heavy landing on a motocross track left him with internal injuries.
Jack Miller left with shoulder and collarbone injury after a mountain bike accident in California.
By Michael Scott
